A ball end mill is used for a machining process of, mainly, a die or the like. A cutting edge of the ball end mill on the tip side forms an arc in a side view. In general, such a ball-nosed end cutting edge on the tip side also forms an arc in an axial view of which a radius of curvature is constant from the inner peripheral portion to the outer peripheral portion. In addition, PTL 1 discloses a ball end mill that includes a first blade section on the inner peripheral side, a second blade section on the intermediate side, and a third blade section on the outer peripheral side of a ball-nosed end cutting edge, in which the radius of curvature of the second blade section is greater than the radius of curvature of the first blade section, and the radius of curvature of the third blade section is less than the radius of curvature of the second blade section, which enables high vibration-proof properties of an end mill body to be achieved.